Chronic inflammation due to viral or bacterial infections has been linked with approximately 15% of cancer-related human deaths. The transcription factor NF-kappaB, a key mediator of this process, is regulated by pro-inflammatory molecules and genotoxic stress. One of several mechanisms by which NF-kappaB may initiate tumor formation is through induction of the inducible nitric oxide synthase (iNOS) leading to production of NO, a molecule important in the suppression of T cell immunity and production of the DNA damaging reactive nitrogen oxide species (RNOS). Myeloid suppressor cells (MSCs) and tumor associated macrophages (TAMs), cells of the myeloid lineage that produce NO and can mediate these effects, infiltrate solid tumors. However mechanisms by which the chronic inflammatory mediator iNOS impacts breast cancer have not been elucidated. Our model, polyomavirus middle T oncogene (PyV-mT) expressed in the mammary epithelium of C57BI/6 mice was used to demonstrate that iNOS promotes tumorigenesis, a finding consistent with human studies associating increased iNOS expression with poor prognosis in breast cancer patients, and anti-inflammatory treatment with reductions in the incidence of breast cancer. The specific hypothesis is that myeloid cells recruited to the mammary gland during chronic inflammation produce iNOS-induced NO that inhibits T cell immunity and causes DNA damage in mammary epithelial cells, important steps in the initiation of cancer. The specific aims to address this hypothesis are: 1) Examine the impact of myeloid cell iNOS induced NO production on mammary tumorigenesis by i) creating a myeloid specific iNOS gene ablation model, ii) characterizing chronic inflammatory cells in wild type and iNOS-/- PyV-mT mice, iii) carrying out reciprocal transplantation experiments, and iv) bone marrow transplantation experiments; 2) Assess iNOS-induced DNA damage to mammary epithelial cells by i) co-culture of myeloid cells and epithelial cells and ii) examination of the p53 DNA damage pathway. This experimental design will enable us to determine the role of myeloid iNOS induced NO in the initiation of mammary tumorigenesis. We also expect to reveal new insights into mechanisms by which chronic inflammation can influence the development of breast cancer and provide a molecular rationale for the use of therapeutics targeting the iNOS/NO pathway. [unreadable] [unreadable] [unreadable]